The invention relates to a micro perfusion device for obtaining at least one constituent of a body fluid by means of a subcutaneously positioned perfusion catheter.
FIG. 7D shows a micro perfusion device as described in “Open-Flow Microperfusion . . . ”, Z. Trajanoski et al., Diabetes Care, Volume 20, Number 7, Jul. 1997, pages 1114 ff. The device comprises a casing 1 which may be fixed to the skin. A flexible, permeable perfusion catheter 5a projects from the casing 1, said catheter being subcutaneously positioned in a tissue 3. A supply catheter 7a for a rinsing liquid—referred to as perfusate in the following—protrudes into the perfusion catheter 5a. The perfusion catheter 5a and the supply catheter 7a form a double-lumen catheter in the tissue 3, comprising an inner lumen within the supply catheter 7a and a surrounding outer lumen between the supply catheter 7a and the perfusion catheter 5a. In the casing 1, the outer lumen feeds into a discharge channel 8 to which a discharge catheter is connected. In order to obtain body fluid from the tissue 3, the perfusate is guided through the supply catheter 7a up close to a front distal end of the perfusion catheter 5a. Once the perfusate has emerged at the front distal of the supply catheter 7a, it flows back along the supply catheter 7a in the outer lumen. A rinsing liquid is used as the perfusate which penetrates the constituent whose concentration in the body fluid is to be ascertained. Furthermore, body fluid is sucked into the outer lumen through the perforated perfusion catheter 5a by the rinsing effect. The mixture of perfusate and body fluid is discharged through the discharge channel 8 to a measuring means. The fluid is conveyed through the device by means of a pump.
The placement procedure prior to the use of the perfusate can be seen from FIGS. 7A to 7D. An injection needle 4a is used to position the device. Before it is positioned, the perfusion catheter 5a tightly surrounds the injection needle 4a. Once the skin has been pierced and the injection needle 4a positioned in the tissue 3 (FIG. 7A), the injection needle 4a is retracted again (FIG. 7B), and the perfusion catheter 5a remains in the tissue in the position shown. The supply catheter 7a is then inserted through the casing 1 into the perfusion catheter 5a (FIG. 7C). It is inserted in the perfusion catheter 5a until it takes up most of the length of the perfusion catheter 5a (FIG. 7D). The front end of the supply catheter 7a is, however, some distance short of the front end of the perfusion catheter 5a. 
Micro perfusion devices of the type described require piercing the skin, retracting the injection needle and subsequently providing a perfusate supply.